The Late Pleistocene European small hamsters

The prevailing paleobiogeographic hypothesis posits that during the Pleistocene, steppe and tundra-steppe taxa currently found in Central Asia expanded into Europe during glacial periods, when open habitats prevailed. However, our previous findings show that European narrow-headed voles (Stenocranius anglicus) diverged from their Asiatic counterparts at least 200,000 years ago, implying their prolonged isolation and survival through at least one interglacial period in European refugia. To investigate whether this was an exception or part of a broader pattern, we analyzed mitochondrial genomes from 33 Late Pleistocene and Holocene remains of small hamsters (subfamily Cricetinae) originating from Central Europe, the Balkans, and Anatolia. Late Pleistocene small cricetids from Europe are typically attributed to the grey dwarf hamster (Nothocricetulus migratorius), a species currently distributed in Western and Central Asia and Eastern Europe. Surprisingly, among the 16 samples from Late Pleistocene Central Europe, only the hairy-footed hamster (Phodopus sungorus), now found in northern Kazakhstan and southern Russia, was identified. Phylogenetic analyses showed these specimens formed a sister clade to the lineage comprising all modern individuals. In contrast, all samples from the Balkans and Anatolia were assigned to N. migratorius. Phylogenetic reconstruction indicated that Holocene samples from Anatolia grouped with modern local populations, while Late Pleistocene samples from the Balkans formed a sister lineage to all extant individuals. In both cases, the divergence of the Late Pleistocene lineages was relatively recent, suggesting population continuity with the Late Pleistocene Asiatic source populations and likely the repeated population expansions, rather than long-term isolation in Europe. Our results suggest that, despite occupying broadly similar ecological niches, steppe species exhibit idiosyncratic responses to past climatic and environmental changes. Consequently, generalizations about their evolutionary histories may be unwarranted.

主流古生物地理假说认为，在更新世（Pleistocene）时期，当前分布于中亚的草原（steppe）与苔原草原（tundra-steppe）类群，在开阔生境占主导的冰川期向欧洲扩张。然而本团队此前的研究结果显示，欧洲狭头田鼠（*Stenocranius anglicus*）至少在20万年前便与其亚洲近缘类群产生分化，这意味着它们在欧洲生物避难所（refugia）中长期隔离并至少度过了一个间冰期（interglacial period）。为探究这一现象是特例还是更广分布模式的一部分，本研究对采自中欧、巴尔干半岛（Balkans）与安纳托利亚（Anatolia）的33件晚更新世（Late Pleistocene）及全新世（Holocene）小型仓鼠（仓鼠亚科Cricetinae）遗骸的线粒体基因组（mitochondrial genomes）进行了分析。欧洲晚更新世小型仓鼠类通常被归为灰侏儒仓鼠（*Nothocricetulus migratorius*），该物种当前分布于西亚、中亚与东欧地区。令人意外的是，在16件采自晚更新世中欧的样本中，仅鉴定出毛足仓鼠（*Phodopus sungorus*）——该物种当前仅分布于哈萨克斯坦北部与俄罗斯南部地区。系统发育分析（phylogenetic analyses）显示，这些标本构成了所有现代个体类群的姊妹支系（sister clade）。与之相反，所有巴尔干半岛与安纳托利亚的样本均被归为*N. migratorius*。系统发育重建结果表明，安纳托利亚的全新世样本与现代当地种群聚为一支，而巴尔干半岛的晚更新世样本则构成所有现存个体的姊妹支系。两种情况下，晚更新世支系的分化时间均相对较近，这表明其种群与晚更新世亚洲源种群存在延续性，且大概率经历了多次种群扩张，而非在欧洲长期隔离。我们的研究结果表明，尽管草原物种占据了大体相似的生态位（ecological niches），但它们对过去气候与环境变化的响应具有特异性。因此，对其演化历史做出泛化推论可能并不妥当。